GROOT

The modern Groot's heroic career began as a Kree prisoner volunteered for a suicide mission: Star-Lord's strike team, infiltrating Phalanx-occupied space in Annihilation: Conquest – Star-Lord Vol. 1 #1–4 (2007). The mission went so badly that Groot stayed behind in a burning passage to buy his new friends their escape and was left for dead — the first time. He survived as a sprig, was replanted, and regrew in a pot on the team's shoulder, considerably shorter and in a considerably worse mood about it.

Then came the Babel Spire, the Phalanx's transmission tower on Hala, and a demolition problem with no conventional solution: the explosives plan had collapsed along with Star-Lord's capture by Ultron. Groot volunteered the alternative his biology made possible. Smuggled into the Spire's sub-basement, he drank in its nutrient-rich fluids while Mantis accelerated his growth, expanding through floor after floor until his own mass was the bomb — and he had deliberately made himself highly flammable, so that when the end came he would burn completely and take the tower's heart with him, in Annihilation: Conquest Vol. 1 #6 (2008).

It worked, at the price the plan always carried: the Spire fell, the Phalanx's grip on the Kree broke, and Groot burned down to almost nothing doing it. Once again Rocket Raccoon kept a twig. Once again the twig took root. The Guardians of the Galaxy who formally assembled in 2008 were built around a tree who had already died for the team twice before the team officially existed — which may explain why nobody in that outfit has ever once questioned his commitment.